Metering exhaust gas recirculation apparatus and system

ABSTRACT

A valve assembly has a spring-loaded pressure responsive diaphragm connected to a stem carrying a valve which is moveable to any of several general operating positions; a chamber in the housing of the valve assembly is exposed to the comparatively low pressure of the interior of the intake manifold of an associated internal combustion engine while the moveable valve is effective for opening and closing an associated port leading to the chamber but operatively connected to a source of exhaust gas of the associated internal combustion engine as, for example, the engine exhaust manifold or, as is often employed, the exhaust cross-over conduit which, generally, physically extends or passes over the associated engine.

Waited; Mates Patent [191 De Martelaere Aug. 13, 1974 [75] Inventor: David L. De Martelaere, Southfield,

Mich.

[73] Assignee: Colt Industries ()perating Corp,

New York, NY.

[22] Filed: Dec. 1, 1972 [21] Appl. No: 311,168

[52] US. C1 123/119 A [51] int. C1. F02m 25/06 [58] Field of Search 123/119 A [56] References Cited UNITED STATES PATENTS 2,722,927 11/1955 Cornelius 123/119 A 3,542,004 11/1970 Cornelius 123/119 A 3,641,989 2/1972 Hill 123/119 A 3,646,923 3/1972 Sarto 123/119 A Thornburgh 123/1 19 A Primary Examiner-Wendell E. Burns [5 7] ABSTRACT I A valve assembly has a spring-loaded pressure responsive diaphragm connected to a stem carrying a valve which is moveable to any of several general operating positions; a chamber in the housing of the valve assembly is exposed to the comparatively low pressure of the interior of the intake manifold of an associated internal combustion engine while the moveable valve is effective for opening and closing an associated port leading to the chamber but operatively connected to a source of exhaust gas of the associated internal combustion engine as, for example, the engine exhaust manifold or, as is often employed, the exhaust crossover conduit which, generally, physically extends or 7 passes over the associated engine.

16 Claims, 7 Drawing Figures 2/1973 Chand et a1. 123/119 A PATENIED ms] 31974 sum 2 are J HJ RESTRICTED FLOW IN INCHES OF VACUUM VALUE IN CHAMBER METERING EXHAUST GAS RECIRCULATION APPARATUS AND SYSTEM BACKGROUND OF THE INVENTION Because of the general concern about pollution, various governmental agencies have set forth regulations on vehicular internal combustion engine exhaust emissions. Generally, nitrous oxide, carbon monoxide and unburned hydrocarbons comprise such undesirable cxhaust emission. The art has developed certain means and methods for substantially reducing the amount of carbon monoxide and unburned hydrocarbons. However, generally, the problem of removing or reducing the nitrous oxide has not heretofore been solved.

It appears that nitrous oxide is formed within the engine combustion chamber during ignition of the fuel and air mixture therein. Also it appears that more nitrous oxide is formed as the temperature within the combustion chamber increases or as the compression ratio of a piston engine is increased.

Accordingly, it has been determined that the quantity of nitrous oxide can be reduced if some inert gas is placed into the combustion chamber along with the fuel-air mixture. This, apparently, results effectively, in lessening the total or maximum temperature during combustion.

It has been discovered that one way of achieving this is to, in effect, recirculate a portion of the engine ex haust gas back into the engine combustion chambers thereby using the carbon dioxide of the exhaust gas to serve as an inert gas.

Accordingly, the invention as herein disclosed and described is primarily directed to the solution of the above problems and the provision of means effective to provide such desired exhaust recirculation.

SUMMARY OF THE INVENTION According to the invention, a valve assembly controlled generally in accordance with throttle valve position is effective to as times meter a particular volume rate of exhaust gas flow from the engine exhaust system back to the engine induction intake manifold. Certain means are provided as to, at certain conditions of engine operation, cause the valve to be totally closed thereby preventing any recirculation of such exhaust gases. Also, means are provided to protect the valve assembly from the relatively high exhaust temperatures.

BRIEF DESCRIPTION OF THE DRAWINGS In the'drawings, wherein for purposes of clarity certain elements and details may be omitted from one or more views:

FIG. 1 is a view illustrating, in simplified form, a carburetor, or other induction device, situated atop the intake manifold of an associated engine with an exhaust gas recirculating valve, constructed in accordance with the teachings of the invention, oper'atively connected thereto;

FIG. 2 is an enlarged generally axial cross-sectional view of the valve assembly shown in elevation in FIG.

FIG. 3 is a view taken generally on the plane of line 3-3 of FIG. 2 and looking in the direction of the arrows;

FIG. 4 is a simplified view, in reduced scale, of the valve assembly of FIG. 2, taken generally on the plane of line 44 of FIG. 2 and looking in the direction of the arrows;

FIGS. 5 and 6 are views similar to FIG. 4 but respectively illustrating elements thereof in varying operating positions different from that shown in FIG. 4; and

FIG. 7 is a graph illustrating a characteristic operating curve of the valve assembly of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now in greater detail to the drawings, FIG. I illustrates an induction device, such as a carburetor I0, situated atop a plate-like spacer member 12 which, in turn, is carried atop the inlet of intake manifold 14 of an associated internal combustion engine. Carburetor l0, spacer 12 and intake manifold 14 may be secured to each other by any suitable means.

As shown, the induction passage means 16 in carburetor 10, which contains a throttle valve means 18 variably positionable as by a rotatable throttle shaft 20, communicates with corresponding induction passage means 22 formed through spacer member 12 which, in turn, communicates with the interior passage means 24 of the intake manifold 14.

The exhaust gas recirculating valve assembly 26 is shown suitably mounted and secured to a projecting portion of plate member 12. A pair of ports or conduits formed in valve assembly 26 respectively communicate with first and second passage means 28 and 30 formed in or defined by spacer plate 12. As generally illustrated, passage 28 is placed in communication with a source of engine exhaust gases as, for example, by conduit means 32 communicating at one end with conduit 28 and communicating at another end with the engine exhaust system as, for example, the interior of the exhaust manifold fragmentarily illustrated at 34, while passage 30 is placed in communication with the interior 24 of the intake manifold as, for example, opening into induction passage portion 22 downstream of the throttle means 18.

Porting means 36, formed in carburetor l0, communicates via conduit means 38 with a chamber of the valve assembly 26. The port 36 is situated in any desireable location with respect to edge 40 of throttle valve 18 so as to create any desired value of vacuum in conduit means 38 during, for example, curb idle with such vacuum value being zero if so desired for the particular engine on which the invention is to be employed.

Referring now in greater detail to FIGS. 2 and 3, the preferred embodiment of valve 26 is illustrated as comprising a valve body 42 having secured thereto a vacuum or pressure operated motor assembly 44. The motor assembly 44 is illustrated as being comprised of housing sections 46 and 48 which cooperate to peripherally secure therebetween, as at 50, a pressure responsive diaphragm member 52 in a manner whereby distinct but variable chambers 54 and 56 are defined at opposite sides thereof with chamber 54 being situated generally within housing section 46 while chamber 56 is located generally within housing section 48.

Generally centrally situated diaphragm backing plates 58 and 60 are located at opposite sides of diaphragm 5 2 and secured thereto as between a shoulder 62 and peened head 64 of a valve stem member 66. A compression spring 68, within chamber 54, operatively engages diaphragm 52 and normally causes it as well as valve stem 66 to be moved to the position illustrated.

Chamber 54, otherwise closed, is placed in communication with conduit means 38 as by a conduit section 72 formed in housing section 46. In contrast,-chamber 56 is conveniently vented to the flow of ambient cooling air as by means of a plurality of vent-like openings 70 formed in the circumferential wall of housing section 48 by stamping and outwardly bending integral tabs 73, which act as cooling fins that may also direct the cooling air into and from the housing. Such cooling is desirable to protect the diaphragm 52 from relatively high exhaust temperatures.

The entire motor assembly 44 may be secured to the valve housing 42 as by spinning a portion 74 of the lower part 76 of housing section 48 so as to have such portion 74 engaged within an annular groove or recess 78 formed generally peripherally about the upper portion of valve body 42.

The lower end of valve body 42 terminates in a mounting surface or surface 80 which, as also shown in FIG. 3, has a pair of conduit or passage portions 82, 84 opening therein as well as a pair of clearance apertures 86, 88 through which, for example, suitable screws (not shown) extend for engaging the spacer body 12 and thereby secure valve body 42 thereto as depicted in FIG. 1.

With respect to FIG. 1, conduit 82, shown in FIGS. 2 and 3, is operationally placed in communication with conduit means 28 and 32 leading to a source of engine exhaust gases 34, while conduit 84 is placed in communication with a suitable source of intake manifold vacuum as by conduit means 30.

Further, conduit portions 82 and 84 each communicate with a general chamber 90 formed within valve body 42. As is shown also by the simplified FIGS. 4, and 6, conduit 84 is in an unrestricted communication with chamber 90 while conduit 82 is, in what may be called, in controlled or valved communication with chamber 90.

The upper end of chamber 90 may be effectively closed as by an annular-like member 92, received and secured within chamber 90 as by press-fitting, along with a plurality of seal and/or thermal barrier washerlike members. For example, preferably, the upper end surface 94 of valve body 42, at a level or elevation spaced from the upper surface of annular member 92, carries thereagainst a steel washer-like member 96 which, in turn, against its opposite side, carries a thermal barrier annular or washer-like member 98 which may be formed as of a suitable fibrous material such as, for example, asbestos. As best shown in FIG. 2, sealing members 96 and 98 are preferably retained in the position illustrated as by generally radially inwardly extending tab portions 100 struck out of the annular wall of housing section 48. As shown tabs 100 resiliently hold the annular members 96 and 98 in assembled relationship.

An additional washer-like member 102, preferably of material such as stainless steel, is situated generally about valve stem 66 and between the upper surface of member 92 and the lower surface of washer member 96. Preferably, there is a slight clearance as between the diameter of valve stem 66 and aperture 104 of member 102 through which such stem passes.

As shown in FIG. 2, the valve stem 66 has a valve member 106 fixedly secured to the lower end thereof so as to have a first valving surface 108 engage a coacting first valve seating surface 110 during the condition depicted. The movement of valve member 106 is generally confined to the area within a chamber-like space 112 defined generally by a cup-like member 114 suitably seated and secured within and by coacting wall portions 116 formed internally of said valve body 42.

The chamber-defining member 114 is illustrated as having an upper aperture 118 as well as at least one radially directed orifice 120 formed through the wall thereof. Although a plurality of such orifices 120 are illustrated, it is contemplated that when the member 114 is secured to the valve body 42, it will be positioned as to have only one orifice 120 in communication between chamber 112 and chamber 90 or conduit 84 as depicted by FIGS. 4, 5 and 6. The upper part of valve member 106 is provided with generally a second valving surface 122 which, as will become apparent, at times functions to constrict and restrict fiow through orifice 118 into chamber 90.

OPERATION OF THE INVENTION The operation of the valve means 26, without regard to its function in the overall system as generally depicted in FIG. 1, is illustrated by FIGS. 4, 5 and 6.

Referring in greater detail to FIG. 4, it can be seen that with atmospheric pressure, P in chamber 56 and the pressure, P in chamber 54 being,'for example, either equal to or insufficiently less than pressure P,, spring 68 will hold the valve member 106 closed against seating surface 110 and thereby prevent communication as between chamber 90 and conduit 82 which, in turn, is in communication with source 34 as via conduit means 32. At this time conduit 84 complete communication between a source of relatively low pressure (in this instance the interior 24 of the intake manifold with the manifold vacuum existing therein) and chamber 90. It should be pointed out that any leakage which might be experienced around valve stem 66 and between chambers 90 and 56 will not-effect pressure P, since the atmospheric vents are sufficient to provide a flow rate to chamber 56 greater than any possible rate of leakage flow.

As the value of P is reduced the pressure differential, AP, (where AP P P finally increases sufficiently to overcome any preload force of spring 68 and as the value of AP continues to increase diaphragm 52, against the resilient resistance of spring 68, moves upwardly carrying the valve stem 66 and valve member 106 with it to some position as generally depicted in FIG. 5. The degree of such upward movement will, of course, depend on the value of AP where P is primarily the variable pressure. During this time, it should be apparent, that flow will occur through both orifice means 118 as well as aperture or orifice means 120. During conditions of operation as generally depicted in FIG. 5, the maximum amount or rate of flow will occur through conduit 82 and into chamber and conduit means 84.

As the value of AP increases valve member 106 is progressively moved upwardly until the upper or second valveing surface 122 finally engages and seats against the upper inner seating surface 124 of member 114, as shown in FIG. 6, thereby terminating any further flow around valve member 106 and through orifice 118. When this condition of operation is attained all flow through conduit 82 must also pass through orifice means 120 and, in the preferred embodiment of the invention, orifice means 120 is calibrated as to provide for sonic flow therethrough when orifice means 118 is closed by valve member 106. Consequently, in the preferred embodiment, regardless of any increase in pressure differential as between conduits 82 and 84, a constant volume flow rate will be maintained through orifice means 120 during the condition depicted by FIG. 6.

Now, considering the operation of the valve assembly 25 within thesystem of FIG. 1 and assuming that the related engine is running at curb idle conditions, it can be seen that, because of the nominally closed position of throttle valve 18, the control of actuating vacuum communicated to chamber 54 via port means 36 and conduit means 38 will be either nil or very little because of the particular location of port means 36 relative to edge 40 of throttle 18. Consequently, the value of P may be near or at the value of atmospheric pressure, P and therefore valve 106 will assume a position as shown in either of FIGS. 2 or 4.

It should be apparent that as throttle valve 18 is rotated clockwise in the opening direction that ports means 36 will be progressively increasingly exposed to the relatively low pressure of the manifold vacuum below the throttle valve 18. It should also be apparent that the throttle valve 18 may be operatively connected to associated valving means in circuit with conduit means communicating between the source of manifold vacuum and chamber 54 and through control of such associated valving means control the degree of such communication. In such a situation the porting means 36 could, of course, be dispensed with. Further, it should be obvious that the porting means 36 illustrated in FIG. 1, may actually comprise a plurality of distinct but pneumatically parallel ports adapted to be generally serially or sequencially traversed by edge 40 of throttle valve 18.

In any event, when the engine undergoes part throttle acceleration a greater control or actuating vacuum is communicated to chamber 54 via conduit means 38. This causes diaphragm 52 and valve 106 to move upwardly opening the flow through conduit 82. The degree of such flow will, of course, be dependent upon the degree of opening movement of valve member 106. As valve 106 is thusly opened, exhaust gas flow through conduit means 32 and 28 starts and passes through conduit 82 into chamber 112 of member 114 and subsequently through orifices 118 and 120 into chamber 90 and conduit 84 from where it flows as through conduit means 30 and into the induction or intake manifold 14. The flow rate of such exhaust gas flow will depend on the degree to which valve member 106 has been opened and the degree to which valve member 106 has been opened will depend on the value of the vacuum communicated to vacuum motor chamber 54, and, of course, the value of the vacuum communicated to chamber 54 will depend on the degree of opening of throttle valve 18.

For example, referring to FIG. 7, during curb idle the degree of vacuum communicated to chamber 54 would be insufficient to initiate opening movement of valve 106. However, as the throttle valve 18 started opening and the value of the vacuum communicated to chamher 54 increased to that, for example, designated 148 in FIG. 7, the valve 106 would start opening with any further increase in throttle opening and consequent increase in actuating vacuum.

If the throttle valve 18 continued to be increasingly means 120. This might be considered as being generally depicted by FIG. 5.

However, as the throttle valve 18 is opened beyond a degree of opening corresponding to point 150, the further resulting upward movement of valve member 106 causes the second or upper valving surface 122 thereof to progressively more nearly approach the inner upper valve seating surface 126 of member 114 and, in so doing, reduce the clearance therebetween so as to exhibit an increasing restrictive effect on the flow of recirculated exhaust gases through orifice means 118. Such increasing restrictive effect by valve 106 and the consequent decrease in the volume rate of flow of recirculated exhaust gases, as the throttle valve 18 is progressively opened beyond the point corresponding to 150, results in a relationship depicted by curve por- In the preferred embodiment of the invention, point 152 is achieved when the throttle valve 18 has been fully opened or to what is commonly referred to as, wide open throttle. At this time sufficient actuating or control vacuum has been communicated to chamber 54 as to cause valve member 106 to be moved upwardly to a position depicted in FIG. 6 wherein further flow of recirculated exhaust gases through orifice means 118 is terminated. Consequently, operation of engine and associated vehicle under wide open throttle regardless of the engine load will not change the volume rate of recirculated exhaust gas flow which will remain at the value depicted by straight-line curve portion C. This being so, of course, because in the preferred embodiment orifice means 120 provide sonic flow when the other orifice means 118 is closed by valve member 106.

In view of the preceding, it should be apparent that when the vehicle engine is experiencing deceleration the valve assembly 26 will assume the condition depicted by either of FIGS. 2 or 4 because during such deceleration the throttle valve 18 will be nominally closed just as at curb-idle (depicted in FIG. 1) and therefore there will be an insufficient actuating vacuum communicated to chamber 54 to maintain valve 106 open against the force of spring 68.

Although only the preferred embodiment of the invention has been disclosed and described it is apparent that other embodiments and modifications of the invention are possible within the scope of the appended claims.

I claim:

ll. An exhaust gas recirculation system for an internal combustion engine having first conduit means for contion B, generally between points and 152, of FIG.

ducting from said engine at least part of the exhaust gases generated by said engine and second inlet conduit means for conducting a combustible fluid to said engine, said system comprising third conduit means generally interconnecting and communicating between said first and second conduit means, valve means for controlling the flow of said exhaust gases from said first conduit means through said third conduit means and into said second conduit means, and motor means effective for at times opening said valve means, said motor means being responsive to a variable signal pressure developed by said engine as indicia of engine operation, said system including at least one fixed-area, constantly-open orifice means interconnecting and communicating between said first and said second conduit means for flowing said exhaust gases when said valve means has closed said third conduit means.

2. A system according to claim 1 wherein said second conduit means has flow therethrough controlled by a variably positionable throttle valve, and wherein the magnitude of said variable signal pressure is dependent upon the position of said throttle valve.

3. A system according to claim 2 wherein said valve means is closed during periods of curb idle engine operation and engine deceleration during which said throttle valve is in a nominally closed position.

4. A system according to claim 3 wherein said valve means is opened to a degree permitting a maximum volume rate of flow of exhaust gases from said first conduit means through said third conduit means and into said second conduit means during periods of engine operation wherein said engine is undergoing acceleration under conditions wherein said throttle valve is partly opened.

5. A system according to claim 4 wherein said valve means is opened to a degree permitting a volume rate of flow of exhaust gases from said first conduit means to said second conduit means less than the said maximum volume rate of flow during periods of engine operation wherein said engine is operating with said throttle valve in a wide open position regardless of engine speed.

6. A system according to claim 5 wherein the said volume rate of flow of exhaust gases during wide open throttle engine operation is determined by passage means calibrated as to provide sonic flow therethrough during such condition of engine operation.

7. A system according to claim 1 wherein said second conduit means has flow therethrough controlled by a variably positionable throttle valve, wherein the magnitude of said variable signal pressure is dependent upon the position of said throttle valve, wherein said motor means comprises pressure responsive diaphragm means, and wherein said variable signal pressure is communicated to said diaphragm means so as to make said diaphragm means directly responsive to said variable signal pressure.

8. A system according to claim 7 wherein said variable signal pressure is communicated to said diaphragm means by fourth conduit means, and wherein said fourth conduit means comprises porting means having an opening communicating with said second conduit means, said opening being so positioned as to be in close proximity to an edge of said throttle valve when said throttle valve is in a nominally closed curb idle position and so as to be generally traversed by said edge of said throttle valve as said throttle valve is rotatably variably positioned toward a more nearly wide open position from said curb idle position.

9. A system according to claim 1 wherein said valve means comprises a housing, an inlet for communicating with said first conduit means, an outlet for communieating with said second conduit means, a variably positioned valve member adapted to at times close said inlet, wherein said motor means comprises a pressure responsive diaphragm operatively connected to said valve member, said orifice means comprising a plurality of orifice means serially situated between said inlet and said outlet, all of said plurality of orifice means being effective to flow said exhaust gases therethrough when said valve member is moved to a first opened position with respect to said inlet, certain of said plurality of orifice means being closed to flowof said exhaust gases therethrough upon said valve member being moved to a maximum opened position with respect to said inlet thereby requiring the remaining of said plurality of orifice means to be the only orifice means for flowing therethrough said exhaust gases.

10. A valve assembly for controlling the rate of flow of exhaust gases in an exhaust recirculation system of an internal combustion engine, comprising valve housing means, an inlet and an outlet formed in said housing, a first valve seat formed generally about said inlet, a valve member, a pressure responsive diaphragm assembly including a pressure chamber for the admission therein of an actuating pressure to act upon said actuating diaphragm member within said diaphragm assembly in order to cause a pressure differential across said diaphragm member, a valve stem operatively interconnecting said diaphragm member and said valve member, a chamber-defining member generally enclosing said valve member and positioned as to be in communication with said inlet when said valve member is moved away from said first valve seat, a plurality of orifices formed through said chamber-defining member and adapted for communication between said inlet and said outlet when said valve member is moved away from said first valve seat, and a second valve seat formed internally of said chamber-defining member, said valve member being effective to engage said second valve seat when said valve member is moved a sufficient distance away from said first valve seat to thereby prevent communication between said inlet and outlet through certain of said plurality of orifices while permitting continued communication between said inlet and outlet through remaining of said plurality of orifices.

11. A valve assembly according to claim 10 wherein said valve housing means comprises a first housing portion for containing said valve member, and a second housing portion for containing said diaphragm assembly and defining said pressure chamber, and further comprising thermal barrier means situated generally between said first and second housing portions in order to reduce the temperature conduction from said first housing portion to said second housing portion.

12. A valve assembly according to claim 10 wherein said pressure chamber is adapted for communication with a source of engine developed vacuum.

13. A valve assembly according to claim 12 and further comprising spring means carried generally within said pressure chamber and operatively engaging said diaphragm member, said spring means normally urging said valve member toward said first valve seat.

14. A valve assembly according to claim 12 and fur- 16. A valve assembly according to claim 15 wherein ther comprising means for cooling said diaphragm. said openings are formed by displacing from the walls 15. A valve assembly according to claim 14, wherein of said housing means integral tabs to provide cooling said cooling means comprises air openings formed in fins that may also direct the cooling air. said valve housing means 5 

1. An exhaust gas recirculation system for an internal combustion engine having first conduit means for conducting from said engine at least part of the exhaust gases generated by said engine and second inlet conduit means for conducting a combustible fluid to said engine, said system comprising third conduit means generally interconnecting and communicating between said first and second conduit means, valve means for controlling the flow of said exhaust gases from said first conduit means through said third conduit means and into said second conduit means, and motor means effective for at times opening said valve means, said motor means being responsive to a variable signal pressure developed by said engine as indicia of engine operation, said system including at least one fixed-area, constantly-open orifice means interconnecting and communicating between said first and said second conduit means for flowing said exhaust gases when said valve means has closed said third conduit means.
 2. A system according to claim 1 wherein said second conduit means has flow therethrough controlled by a variably positionable throttle valve, and wherein the magnitude of said variable signal pressure is dependent upon the position of said throttle valve.
 3. A system according to claim 2 wherein said valve means is closed during periods of curb idle engine operation and engine deceleration during which said throttle valve is in a nominally closed position.
 4. A system according to claim 3 wherein said valve means is opened to a degree permitting a maximum volume rate of flow of exhaust gases from said first conduit means through said third conduit means and into said second conduit means during periods of engine operation wherein said engine is undergoing acceleration under conditions wherein said throttle valve is partly opened.
 5. A system according to claim 4 wherein said valve means is opened to a degree permitting a volume rate of flow of exhaust gases from said first conduit means to said second conduit means less than the said maximum volume rate of flow during periods of engine operation wherein said engine is operating with said throttle valve in a wide open position regardless of engine speed.
 6. A system according to claim 5 wherein the said volume rate of flow of exhaust gases during wide open throttle engine operation is determined by passage means calibrated as to provide sonic flow therethrough during such condition of engine operation.
 7. A system according to claim 1 wherein said second conduit means has flow therethrough controlled by a variably positionable throttle valve, wherein the magnitude of said variable signal pressure is dependent upon the position of said throttle valve, wherein said motor means comprises pressure responsive diaphragm means, and wherein said variable signal pressure is communicated to said diaphragm means so as to make said diaphragm means directly responsive to said variable signal pressure.
 8. A system according to claim 7 wherein said variable signal pressure is communicated to said diaphragm means by fourth conduit means, and wherein said fourth condUit means comprises porting means having an opening communicating with said second conduit means, said opening being so positioned as to be in close proximity to an edge of said throttle valve when said throttle valve is in a nominally closed curb idle position and so as to be generally traversed by said edge of said throttle valve as said throttle valve is rotatably variably positioned toward a more nearly wide open position from said curb idle position.
 9. A system according to claim 1 wherein said valve means comprises a housing, an inlet for communicating with said first conduit means, an outlet for communicating with said second conduit means, a variably positioned valve member adapted to at times close said inlet, wherein said motor means comprises a pressure responsive diaphragm operatively connected to said valve member, said orifice means comprising a plurality of orifice means serially situated between said inlet and said outlet, all of said plurality of orifice means being effective to flow said exhaust gases therethrough when said valve member is moved to a first opened position with respect to said inlet, certain of said plurality of orifice means being closed to flow of said exhaust gases therethrough upon said valve member being moved to a maximum opened position with respect to said inlet thereby requiring the remaining of said plurality of orifice means to be the only orifice means for flowing therethrough said exhaust gases.
 10. A valve assembly for controlling the rate of flow of exhaust gases in an exhaust recirculation system of an internal combustion engine, comprising valve housing means, an inlet and an outlet formed in said housing, a first valve seat formed generally about said inlet, a valve member, a pressure responsive diaphragm assembly including a pressure chamber for the admission therein of an actuating pressure to act upon said actuating diaphragm member within said diaphragm assembly in order to cause a pressure differential across said diaphragm member, a valve stem operatively interconnecting said diaphragm member and said valve member, a chamber-defining member generally enclosing said valve member and positioned as to be in communication with said inlet when said valve member is moved away from said first valve seat, a plurality of orifices formed through said chamber-defining member and adapted for communication between said inlet and said outlet when said valve member is moved away from said first valve seat, and a second valve seat formed internally of said chamber-defining member, said valve member being effective to engage said second valve seat when said valve member is moved a sufficient distance away from said first valve seat to thereby prevent communication between said inlet and outlet through certain of said plurality of orifices while permitting continued communication between said inlet and outlet through remaining of said plurality of orifices.
 11. A valve assembly according to claim 10 wherein said valve housing means comprises a first housing portion for containing said valve member, and a second housing portion for containing said diaphragm assembly and defining said pressure chamber, and further comprising thermal barrier means situated generally between said first and second housing portions in order to reduce the temperature conduction from said first housing portion to said second housing portion.
 12. A valve assembly according to claim 10 wherein said pressure chamber is adapted for communication with a source of engine developed vacuum.
 13. A valve assembly according to claim 12 and further comprising spring means carried generally within said pressure chamber and operatively engaging said diaphragm member, said spring means normally urging said valve member toward said first valve seat.
 14. A valve assembly according to claim 12 and further comprising means for cooling said diaphragm.
 15. A valve assembly according to claim 14, wherein said cooling means comprises air openings formed in said valve housing means.
 16. A valve assembly according to claim 15 wherein said openings are formed by displacing from the walls of said housing means integral tabs to provide cooling fins that may also direct the cooling air. 